Polychlorinated biphenyls, or PCBs, were manufactured from 1929 to 1978. The manufacture of polychlorinated biphenyls has been banned in the United States since 1978. These chemicals have been widely used in capacitors, transformers, carbonless carbon paper, hydraulic pumps, vacuum pumps, heat transfer fluids, plasticizers, lubricants, caulking compounds, inks, paints and insect sprays. The major application of PCBs has been in large electrical capacitors and transformers. It has been estimated that over 800 million pounds of PCBs have been produced. A tremendous amount of these chemicals, suspected of causing cancer and birth defects, have been dumped over a number of years, either accidentally or deliberately, in an entirely reckless fashion. Commonly, these chemicals were dumped on land and in lakes, streams and waterways where they eventually collected in the bottom material in considerable concentrations.
The accumulation of PCBs in human and animal tissue and their toxic effects have been well documented. Further, PCBs are a significant hazard to the environment and their disposal has caused great concern. Incineration and land burial have been the main methods of PCB disposal. However, while incineration has been demonstrated somewhat effective for liquid contaminated PCBs, incineration of solid wastes containing PCBs has not been as successful (Federal Register, Vol. 41, No. 64, Apr. 1, 1976). There has, however, been acceptable incineration of solid wastes containing PCBs. Accordingly, most solids containing PCBs, such as waterway sludge, had to be buried in a chemical waste landfill. The great volume of sludge for transportation and burial represents a tremendous cost for such PCB disposal.
Because of the method of dumping toxic chemicals such as PCBs, a tremendous mass of soil has been contaminated. In the past, bottom soils or the like contaminated with these toxic organic fluids have been treated by attempting to burn or by burying them. Because of the nature of the materials in which the PCB contamination is often found, burning is extremely difficult and expensive and burying is often only a stop gap measure. Many microorganisms have been reported that can degrade PCBs to some degree. The limited information presently available indicates that PCBs have a strong affinity for soil.
It has been recognized that thermal decomposition of polychlorinated organic compounds is possible despite the very high degree of thermal stability of these compounds. U.S. Pat. No. 4,140,066 discloses a method of decomposing PCBs by exposure to heat in a combustion chamber which operates with extremely intense turbulence and pulsation under temperatures as low as 850.degree. C. and with residence times as short as 0.1 second. However, the patent provides no method or apparatus for dealing with the problem of the treatment of mountainous amounts of contaminated, wet material having a relatively low heating value. Thus, while the method set forth in the '066 patent may be highly useful in eliminating PCB containing compounds in relatively small volumes, the process is not particularly helpful in dealing with contaminations on the order of tons in the form of residues in solids such as sludge.
A variety of techniques for incinerating waste material are known. The following U.S. patents are exemplary: U.S. Pat. Nos. 4,245,570; 3,858,534; 3,829,558; 3,812,794; 3,716,339; and 3,511,194. In accordance with related prior patents U.S. Pat. Nos. 4,402,274; 4,463,691; 4,685,220; 4,699,721; 4,778,606 and 4,793,937, all six patents hereby incorporated by reference, PCBs and other hazardous or toxic organic compounds are very effectively and efficiently separated from fluidizable solid materials, but the concentrated toxic material must then be handled for disposal, such as by burial or incineration. In accordance with the present invention, the vaporized toxic material is conveyed to an electrochemical cell for oxidation of the toxic material, after separation by vaporization, and optionally some intermediate processing steps, such as separation of entrained solid materials, to provide a complete, self-contained process for both removal of the toxic material, and treatment of the toxics to render them less toxic or hazardous or non-toxic or non-hazardous. Alternatively, or in addition to the treatment of the vapor in the electrochemical cell, liquid containing organic contaminants, such as PCBs can be conveyed through an electrochemical cell for oxidation of the toxic or hazardous organic contaminants contained in the liquid. The method and apparatus of the present invention are particularly effective for removal and chemical conversion of toxic or hazardous hydrocarbons from a fluidizable solid material, such as a sludge e.g., sand, clay, diatomaceous earth, charcoals, carbon, coals, silicas, alumina, silica-aluminas, metal particulates, metallic ores, and artificial sludges, such as those resulting from industrial spill absorption of liquids into an absorbent material. Once the toxic or hazardous material has been separated from the host material, or separated from other solids, the toxic or hazardous material can be stored as a liquid.
The electrochemical cell utilized in accordance with the present invention is fully disclosed in U.S. Pat. No. 3,616,339, hereby incorporated by reference. While U.S. Pat. No. 3,616,339 discloses that the cell is useful for oxidation of air impurities, such as cigar and cigarette smoke and other aromatic and unsaturated hydrocarbons to remove odors from air, the patent does not disclose or suggest the use of the cell for chemical reaction of toxic or hazardous substances such as PCBs and dioxin or that it is useful for removal of contaminants in liquid form.